Chlorophyceae (hereinafter, referred to as ‘green algae’) includeprocaryota (that is, blue-green algae) and eucaryota (that is, most of green algae), and have in general a photosynthetic pigment and are autotrophic like as plants. In other words, it is known that green algae generate oil and efficient ingredients by photosynthesis using light and carbon dioxide. Blue-green and green algae may occur a blooming to cause water contamination, however, are currently cultured in laboratories and fields for purposes of producing health substances such as EPA, DHA, etc., as well as useful carotinoid-based pigments present in cells of green algae. Furthermore, culturing green algae with a high lipid content may produce FAME (biodiesel) possibly used as a biofuel, thus coming into the spotlight.
In a process of manufacturing algal (green algal) biodiesel, in particular, in downstream processes (culture, harvest/drying, extraction, and conversion to biodiesel), one among significant parts to reduce costs is green algae harvest. In particular, great energy is intensively required to harvest small cells (1 to 10 μm) from an extremely diluted solution, which is a significant problem that has yet to be overcome. Accordingly, there is still no certain way for rapidly and effectively harvesting green algae.
At present, techniques reported in the art may include, for example, centrifugation, flocculation, filtration, floating, pH control (to pH 11), or electrolysis method. However, these are energy consuming techniques, and it is not easy to use equipments for increasing efficiency thereof. Even though electrolysis method has better advantages, compared to other methods, this is a technique based on leakage of Al3+ ions due to use of an electrode and application thereof, hence being cumbersome in use. Accordingly, development of appropriate techniques is still needed.
For flocculation method, use of existing cationic polymer or bioflocculant (bio-flocculation agent) produced by microorganisms has been reported. However, forms of water-soluble molecular ion and polymer have decreased efficiency. In order to effectively harvest the green algae, as a positive value of zeta-potential of a molecule is concerned, the bigger the better. Furthermore, if the flocculant has strong cationic properties at a pH level ranging from 7 to 10 similar to conditions for green algae culture, green algae may be effectively harvested through flocculation. The reason for this is because the surface of green algae exhibits anionic properties. Furthermore, when using a flocculant in a particle form rather than ionic status, it is possible to find an alternative way capable of more effectively applying the flocculant and recovering the same. If the flocculant can be mass-produced and does not have residual toxicity, medium nutrients may be used in re-culture of green algae, thus considerably reducing unit cost of a product.
Accordingly, in order to solve the above-described problems, there is a need for a novel inventive flocculant in a particle type to rapidly and effectively harvest (that is, flocculation/sedimentation) the green algae.